The present invention relates to a chuck-integrated force-measuring system for determining cutting forces at the cutting-tool tip of a rotating tool having at least one measuring sensor, as well as a measured-value processing station.
When working with machine tools, such as NC machines, the execution of a machining process, for example the cutting removal of material by turning, drilling, milling, broaching, etc., is reflected in the time sequence of specific physical quantities, such as the cutting force and/or feed force. By recording and evaluating these quantities, the process can then be monitored with regard to the quality of the result (intelligent analysis of measurement signals). On this basis, it is likewise possible to control the process by considering specific, variable process parameters, such as speed, feed force, respectively feed rate, etc., in accordance with specific criteria, for example machining quality, machining time, etc., as well as in accordance with a combination of such criteria.
In this case, the force that is exerted at the machining point (or the cutting edge) of the tool on the workpiece is considered to be a particularly important, information-bearing physical quantity. It is important to know this cutting force as precisely as possible in terms of magnitude and direction, also in the context of those machining methods which employ rotating spindles (for example, drilling, milling, etc.). Of primary importance in this context is the magnitude of the force—also of interest is the resulting direction in the fixed coordinate system.
A fundamental difficulty arises with regard to recording this force using measuring technology. The force is generated at the point of cutting engagement with an instantaneous magnitude and direction that are dependent on the cutting geometry and the control thereof relative to the workpiece surface and the contour thereof.
A complete acquisition of the resulting force requires determining the same in three directions in the fixed coordinate system. This can be accomplished theoretically due to the physical law of “actio=reactio,” using the appropriate measuring sensors either on the workpiece or the tool. In practice, however, there are substantial differences in the measuring results.
From a technical standpoint, it is easily feasible to provide a mounting attachment to accommodate the measuring sensors on the workpiece. However, it is not economically practical in production practice since the workpiece must be clamped on a special measuring table having installed force sensors. Moreover, particularly in the context of dynamic forces, on the one hand, the mass of the workpiece functions as a low-pass filter which attenuates the higher-frequency signal content and, on the other hand, the necessarily finite mass of the measuring table falsifies the signal. Depending on the size of the masses involved, these effects limit the validity of the measurement to a specific frequency band or even preclude a direct analysis without having to first perform a complex model analysis of the entire system.
If the force measurement is carried out at the tool in order to avoid the above problems, the following difficulties arise:
Direct measurements using force sensors at the cutting-tool tip, for example, necessitate appropriate structural design measures for the machine tool. Thus, an appropriate installation space for the measuring technology is to be provided, which is not sufficiently available when working with conventional machining equipment. Therefore, at the present time, these types of measurements are performed, at most, in highly specialized laboratory systems, which can only be used under very restrictive conditions and, therefore, have only little practical significance.
Thus, from the related art in accordance with the enclosed FIG. 1, what is generally referred to as a tool-torque sensing system for drilling machines is known, which is composed of a rotor 60 that is attachable to the spindle of a tool holder, and of a stator 62 which is mounted in a contactless configuration around the rotor 60. The rotor 60 measures the torque that is applied to the rotating drilling tool and transmits the measured values in a contactless process to the stator 62. Moreover, it is optionally possible to also pick off the feed force at the tool holder spindle.
As is discernible from FIG. 1, the rotor 60 is located at the output spindle of the machine tool above the tool chuck. Thus, this related art also requires that an appropriate space be provided for attaching the rotor 60.
In the light of this related art, an object of the present invention is to provide a force-measuring system, in particular for machine tools having a rotating spindle, which will offer an enhanced functionality, for instance in terms of a more comprehensive usability and more precise measuring results.